Coming from the Portland area, take I-84 east to Cascade Locks and cross the Columbia River via the Bridge of the Gods. Across the bridge, turn right on Hwy 14 and follow it east ~6mi to the turn off to Carson (signed) on Hwy 30. From the junction, continue north ~14.5mi turning off onto Wind River Road (signed for Mt. St. Helens) and continue another 16mi to Lone Butte Road. Continue on a good gravel road for ~8mi, again turning right on gravel FR 24 and continue ahead about 4.2mi to the the trailhead at the Cultis Creek campground. (Be sure you're starting at the right trailhead -- the northern trail leaves just outside the campground; the Cultis Creek trail leaves from a parking area inside the campground.)
Cultis Lake to the Bird Mountain Trail:
From the Cultis Creek campground, hike Trail 33 (Indian Heaven or Cultish Creek trail) for ~2.2mi to reach Cultis Lake. From here turn right off the trail and begin the traverse, traveling cross-country wherever the going is easiest. Continue roughly northwest to gain the ridge, and head north, always heading up, to reach Point 5618 -- a rock outcropping and short fun class 3 scramble.
From the top, you'll be able to get a better view of the route ahead. Drop back down the northwest ridge from Point 5618 and continue northwest and up to the grassy open summit of Bird Mountain. Enjoy excellent views of Mt. Adams and other Cascade peaks from here before continuing on down the north ridge. Skirt on the east side for the easiest going past the Bird Pinnacles and continue along the ridge for another short very easy scramble up to the top of Point 5568. Descending off the northern side is the hardest part of this route as the terrain gets steep and pretty thrashy. Again, head down wherever is easiest and stay on the ridge as much as possible; there appeared to be old remnants of a trail in here that would come and go. Continuing north you'll eventually reach the Bird Mountain trail somewhere near the saddle. Fortunately this brushy stretch is not that long. From the saddle, descend east a mile or so back to the Cultis Creek campground.
There is another high point along Bird Mountain's ridge just north of the saddle, but I didn't have time to explore this one. The PCT bypasses it on the west, but it looks like you could just continue on along the ridge and connect up with it on the north side.
Good boots, possibly long pants for brush. Mosquito repellant!